ICD-10-CM – Overview, Significance and Top Diagnostic Codes

by | Published on Nov 18, 2015 | Resources, Medical Coding News (A) | 0 comments

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As the ICD-10 medical coding system officially went live on October 1, all HIPAA covered healthcare settings are required to replace ICD-9-CM codes with ICD-10-CM codes on their claims (date of service from October 1). This significant replacement will have a serious impact on reimbursement and claim processes. Apart from ensuring thorough preparation, healthcare providers should remain very cautious when using ICD-10-CM codes in place of ICD-9-CM. Let’s take a brief look at the new coding system, its significance and the codes you may need to use frequently.

The ICD-10-CM coding system differs from ICD-9-CM in terms of three factors – volume, structure and new features.


If ICD-9-CM has 14,025 diagnosis codes, there are about 69,823 codes in ICD-10-CM. This significant increase in the volume of codes is due to the greater level of detail in ICD-10. Apart from more number of codes, payers and coders face another big challenge that there is not a one-to-one correlation of the codes.


ICD-9 has three to five characters, which represent the following:

  • First three characters (first character numeric or alpha, E or V, and rest of them are numeric) represents Category
  • Last two characters (all of them are numeric) represents etiology, anatomic site and manifestation

On the other hand, ICD-10 has three to seven characters with second character always numeric and three to seven characters either numeric or alpha. The structure represents the following:

  • First three characters (first character alpha except U) represents category
  • Among the last four characters, first three characters represent etiology, anatomic site and severity and the last character is the code extension for obstetrics, injuries and external causes of injury

New Features

  • There are combination codes in ICD-10-CM for certain conditions and associated symptoms
  • You should consider laterality (left, right and bilateral) for selecting the most appropriate ICD-10 code
  • You can find significant expansion of codes in case of injuries, diabetes, alcohol and substance use and post-operative complications
  • Injuries are grouped according to the anatomical site instead of category
  • Certain diseases are reclassified in ICD-10-CM to reflect current medical knowledge
  • You should represent the letter “O” as “O”, not 0 (zero)

Importance of ICD-10-CM

Compared to ICD-9-CM, the new ICD-10-CM coding system has the following advantages:

  • Unlike limited data about patients’ medical conditions with ICD-9, ICD-10 demand higher level of specificity and clinical detail.
  • ICD-10 enhances the capture of advances in medical technology
  • The new coding system updated the medical terminology and classification of diseases according to current clinical practice

This will improve the quality of data and better support several important healthcare needs including:

  • Measuring the quality, safety and efficiency of healthcare provided
  • Monitoring resource utilization
  • Preventing and identifying healthcare fraud and abuse
  • Conducting epidemiological studies, research and clinical trials
  • Designing payment systems and process claims for reimbursement
  • Tracking public health conditions (complications, anatomical location)
  • Enhancing clinical, financial and administrative performance
  • Operational and strategic planning as well as designing healthcare delivery systems

Key ICD-10-CM Codes

Here the ICD-10-CM codes that are used for reporting the most common diseases.

  • I10: Essential (primary) hypertension
  • E11.9: Type 2 diabetes mellitus without complications
  • E78.5: Hyperlipidemia, unspecified
  • M54.5: Low back pain
  • F41.9: Anxiety disorder, unspecified
  • E03.9: Hypothyroidism, unspecified
  • K21.9: Gastro-esophageal reflux disease without esophagitis
  • Z00.00: Encounter for general adult medical examination without abnormal findings
  • F32.9: Major depressive disorder, single episode, unspecified
  • E66.9: Obesity, unspecified

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